In the microanatomy of adult compact human bone the most significant structural units are osteons. On the basis of research currently being conducted by the principal investigator, it appears that biological aging affects osteon morphology as well as the overall life cycle and physiological potential of osteons. Using a multidisciplinary approach including histology, crystallography, protein chemistry, and electron microprobe analysis, the principal investigator proposes a two year research prgram to clarify the processes which produce these effects. Research goals for the program are as follows: 1. Clarify the relationship between aging and the osteon remodeling sequence. 2. Conduct micrometric and crystallographic studies on a site within the osteon which may be active in mineral homeostasis. 3. Conduct dispersive and non-dispersive electron microprobe analysis of organic and inorganic components as sites in the osteons which may be metabolically active. 4. Conduct careful crystallographic analyses of the osteon mineral phase to determine the effect of age on osteon crystal structure. 5. Obtain additional data on the effect of age on amino acid residues in osteoid protein to correlate age-associated changes in the organic phase with those in the mineral phase.